Image texture is a useful characteristic for object differentiation. However, image texture is a difficult characteristic to describe without using some kind of comparison to already familiar objects. Thus, human analysis of image texture is highly subjective. A computer based texture analysis method has the potential to provide a quantitative, and therefore more useful, measure of texture.
Once a textured object is in digital form the problem of analysis becomes a mathematical problem rather than the verbal problem of description. The mathematical problem has proven to be no less intractable.
The problem of image analysis has traditionally been approached as an analysis of visual images or pictures of macroscopic objects, such as crops or forests, or microscopic objects such as stained tissues or cells. However, the principles of texture analysis are applicable to any image be it visual, acoustic or otherwise. Image texture can be qualitatively evaluated as having one or more of the properties of fineness, coarseness, smoothness, granulation, randomness, lineation or being mottled, irregular or hummocky. These are relative terms, a useful analysis of the characteristics of an image must include an absolute measurement of image properties.
In general terms, the approaches to texture analysis can be divided into three primary techniques, these are: statistical, structural and spectral. Statistical techniques include first order approaches such as autocorrelation functions and higher order approaches such as gray-tone spatial-dependence matrices (see Haralick, Shanmugan & Dinstein; “Textural features for image classification”, IEEE Transactions on Systems, Man and Cybernetics SMC-3(6), 610-621; 1973). Structural techniques include the use of primitives and spatial relationships (see Haralick; “Statistical and structural approaches to texture”, Proceedings of the IEEE 67(5), 786-804; 1979). The main spectral technique is Fourier analysis.
There are five steps in image processing. These steps are image acquisition, preprocessing, segmentation, representation and description, and recognition and interpretation. The invention falls into the step of representation and description. Persons skilled in the art will be aware of existing techniques for performing the remaining four steps of image processing.
A general explanation of the prior art relevant to texture analysis can be found in Chapter 9 of “Vision in Man and Machine” by Levine, M; McGraw-Hill, Kew York (1985). Despite research in the area of texture analysis no single method has been developed that completely describes texture either verbally or mathematically.
Abdel-Mottaleb makes mention of texture analysis in U.S. Pat. No. 5,768,333, as a technique for second stage discrimination of objects. While, Abdel-Mottaleb makes use of a large number of gray level thresholds, image texture is then characterised by computing many features of each connected component in the resulting threshold separately, no 2-dimensional surface is formed.